Chapter 15: Support, Movement, and Responses - Science

Stimulants Any substance that speeds up
the activity of the central nervous system is
called a stimulant. Caffeine is a stimulant
found in coffee, tea, cocoa, and many soft
drinks, as shown in Figure 22. Too much
caffeine can increase heart rate and aggravates
restlessness, tremors, and insomnia in
some people. It also can stimulate the kidneys
to produce more urine.
Do you remember reading at the beginning
of this section about being frightened
after a lamp was broken? Think again about
that scare. The organs of your nervous system
control and coordinate responses to
maintain homeostasis within your body.
This task might be more difficult when your
body must cope with the effects of drugs.
Summary
How the Nervous System Works
• The
nervous system responds to stimuli to
maintain homeostasis.
•Nerve Cells
Neurons are the basic functioning units of the
•
nervous system.
To move from one neuron to another, an
impulse crosses a synapse.
•The Divisions of the Nervous System
The autonomic system controls involuntary
•
actions like heart rate and breathing.
The somatic system controls voluntary
actions.
•Safety and the Nervous System
Reflex responses are automatic and are controlled
by the spinal cord.
•The Senses
Sense organs respond to stimuli and work
together to maintain homeostasis.
•Drugs Affect the Nervous System
Drugs can slow or stimulate your nervous
system.
green.msscience.com/self_check_quiz
Figure 22 Caffeine, a substance found in colas, coffee,
chocolate, and some teas, can cause excitability and
sleeplessness.
Self Check
1. Draw and label the parts of a neuron and describe the
function of each part.
2. Name the sensory receptors for the eyes, ears, and
nose.
3. Compare and contrast the central and peripheral nervous
systems.
4. Explain why you have trouble falling asleep after drinking
several cups of hot cocoa.
5. Identify the role of saliva in tasting.
6. Explain why is it important to have sensory receptors
for pain and pressure in your internal organs.
7. Think Critically Explain why many medications caution
the consumer not to operate heavy machinery.
8. Communicate Write a paragraph in your Science
Journal that describes what each of the following
objects would feel like: ice cube, snake, silk blouse,
sandpaper, jelly, and smooth rock.
9. Make and Use Tables Organize the information on
senses in a table that names the sense organs and
which stimuli they respond to.
SECTION 4 The Nervous System 457
Michael Newman/PhotoEdit, Inc.